1. Field of the Invention
The present invention relates to a plasma processing apparatus or a plasma processing method for processing a semiconductor wafer 212 by using plasma to form a wiring structure of a semiconductor device, and in particular, to the plasma processing apparatus or processing method for etching a film structure having films of multiple layers, i.e. films for insulating upper and lower films for forming the wiring structure placed on a surface of the semiconductor wafer 212 put on a sample stage placed in a vacuum vessel which is rendered low-pressure.
2. Description of the Related Art
In recent years, there has been great progress in the trend toward higher integration of semiconductor integrated circuit devices. As for MOS (Metal Oxide Semiconductor) type semiconductor devices, elements such as transistors are becoming miniaturized and higher-performance. In particular, a gate insulating film as one of the elements constituting a MOS structure is rapidly becoming thinner to cope with miniaturization, fast operation and lowered voltage of the transistors.
As for a material constituting the gate insulating film, a silicon dioxide film (SiO2 film) has been conventionally used. On the other hand, if the gate insulating film further becomes thinner in conjunction with miniaturization of gate electrodes, a tunneling current generated by direct tunneling of carriers (electrons and holes) through the gate insulating film, i.e. a gate leakage current increases. For instance, a film thickness of the gate insulating film required by a device of a 130-nm node is 2 nm or so in the case of the SiO2 film. However, this area is the area where the tunneling current starts to flow. Therefore, in the case where the SiO2 film is used as the gate insulating film, the gate leakage current cannot be controlled so that power consumption increases.
Thus, a research is underway to use a material of higher permittivity as the gate insulating film instead of the SiO2 film. As for an insulating film of high permittivity (hereinafter referred to as a high-k film or a hi-k film), a TiO2 film, a Ta2O5 film and an Al2O5 film were conventionally considered. Recently, an HfO2 film, an HfAlOx film, an HfSiOx film and the like are receiving attention because of excellent stability on silicon.
Conditions for processing such a high-k film are disclosed in Japanese Patent Laid-Open Publication No. 2005-45126 (Patent Document 1) for instance. The conventional technology thereby disclosed specifies a range of gas composition and plasma density when etching a film structure composed of a resist pattern, an antireflection film, a silicon (polysilicon) film, a high-k film, an insulating film (SiO2 film) and the like formed on a silicon substrate by using gases including BC 13 and Ar so as to suppress side etching of the silicon film for a gate and improve accuracy of its shape.
In the case of the conventional technology, however, sufficient consideration was not given to a condition for stably performing the processing and thereby improving reproducibility although it disclosed the condition for improving controllability of the shape by etching a multilayer film including high-k. For instance, attention was not sufficient as to pressure in a processing room and a temperature condition of a sample, a sample stage and a member constituting the processing room when processing a substrate-like sample such as a semiconductor wafer 212 put on a platform in the processing room which is placed in a vacuum vessel.
To be more specific, the temperature condition on the processing is strict as to the film structure using the multilayer film for forming the miniaturized wiring structure such as a high-k and metal gate film. Unless the processing is performed while precisely realizing these, an etching rate or accuracy of the shape becomes low so that processing efficiency and yield will be damaged. This is because these film materials have lower reactivity than the silicon (polysilicon) film which is a film for realizing a conventional gate structure. To improve processing speed by increasing the reactivity, it is inevitable to increase the temperature on the surface of the sample being processed.
When the processing was performed by raising the temperature on the surface of the sample, there was a problem that a photoresist film as a mask placed over the film to be the film structure deteriorated by softening, deformation or the like so that functions as the mask lowered and the shape could not be realized with high accuracy. Furthermore, when high-frequency power supplied to the electrodes in the sample stage for the sake of forming a bias potential is increased in order to raise the temperature for the purposes of increasing the processing speed and improve controllability of the shape, there was a problem that charging damage on the film structure increases during the processing or etching of the upper mask increases.
Furthermore, when performing the processing as the film structure including the film composed of high-melting metal materials, reaction products including chemical compounds of these materials generated then reattach to the surfaces of members constituting inner walls of the processing room and become accumulated in the case where the temperature of the processing room is lower than the temperature of k and the surface of the sample. As for the accumulated products, there is a possibility that they are peeled off by change of the temperature or an interaction with plasma and attach to the surface of the sample to be a foreign substance. Therefore, it becomes necessary to suppress the attachment of the products. To be more specific, it is necessary to raise the temperature of the inner walls of the processing room to be higher than the temperature of the sample stage. In the case of performing the processing at high temperature to improve the efficiency as described above, however, it requires a structure for further raising the temperature of the inner walls of the processing room so that the structure of the processing device becomes larger and more complicated, resulting in higher manufacturing costs. In the case where an outer surface of the vacuum vessel exceeded 50° C., there was a problem that it required facilities for safety as well as installation of a heat insulating material therefor so that extra facilities are required and installation space is required, leading to increased installation costs.
An object of the preset invention is to provide a plasma processing apparatus or a plasma processing method that can etch a multilayer film structure for constituting the gate structure with high accuracy and high efficiency or to provide a plasma processing apparatus of a simple configuration at low cost.